Our overall goal is to create and test a new generation of cell/tissue- targeted MRI contrast agents based on protein cage nanoparticles (PCNs). The aim is to significantly increase the ability to detect and image molecular level events in vascular disease in vivo. This proposal is a multidisciplinary effort, combining established expertise in cardiovascular medicine, vascular biology, MRI, virology, synthetic inorganic and nano-materials chemistry. Based on strong preliminary results, both in vitro and in vivo, our approach will combine the use of bacteriophage P22 capsids as biotemplates for construction of high performance multifunctional MR contrast agents. The interior surface of the P22-based protein cage nanoparticles (PCN) will be used to spatially confine a unique family of polymeric high performance Gd-based T1 contrast agents. The exterior of the PCN will be used for multivalent display of cell-specific targeting ligands and additional in vivo selection and optimization of tissue targeting and blood half-life. The advantage of this approach is a substantial control over the physical parameters required to optimize relaxivity while at the same time incorporating effective tissue targeting and the potential for in vivo discovery in a single system. While these platforms can be applied to a broad range of diseases, the focus of this application will be on vascular disease (atherosclerosis). The specific objectives of this proposal are (i) the development of protein cage nanoparticle-based contrast agents with optimized relaxivity profiles and, (ii) the incorporation of tissue specific targeting ligands to the PCN and in vivo selection of phage for tissue targeting and extended blood half-life, and (iii) the translation of targeted protein cage nanoparticles to image vascular diseases in established mouse models. Issues of Gd toxicity and P22 immunogenicity will also be evaluated. Direct screening of the P22 phage library against fresh human tissue provides an alternative approach for identifying novel tissue-trophic peptides. Creation and evaluation of these PCN-based materials as functional MR contrast agents using state-of the-art facilities will provide rapid and direct feedback for an iterative process to create the next generation of high performance functional MRI contrast agents. The project is collaboration between three groups who have a history of substantial collaboration; Douglas (MSU), McConnell (Stanford University), and Privilege (University of Alabama). Others including Frank (NIH), Dalman (Stanford), Tsao (Stanford), Contag (Stanford), Uchida (MSU), and Zajac (Alabama) will participate as either collaborators or consultants and together this team gathers the breadth of expertise and experience necessary for the successful completion of the stated goals.